The present invention relates to a protective gas pre-flow time control system of gas metal arc welder.
In general, a gas metal arc welding means a welding method in which an arc is generated between a continuously fed consumable type electrode wire and a base material, a shielding gas, such as, CO.sub.2, argon, CO.sub.2 +argon, and the like, is jetted through a gas nozzle set at front end of welding torch for shielding the arc and a welded base material whereby a surrounding air is pushed out and isolated, so that an oxidation and nitration, within the welded metal, is shielded and thereby a good welded portion is made.
In order to normally execute this gas metal arc welding work, the arc welded base material should be shielded by continuously feeding a shielding gas of appropriate purity, through a gas nozzle, from immediately after an arc generation up to the welded base material is congealed after the arc is extinguished.
In accordance with this welder, as shown in FIGS. 1(A) and (B), in case when a distance between a gas nozzle of welding torch and a solenoid valve controlling a shielding gas flow is remoter than approximately 6 m, and, as in FIG. (C), in case where a shielding gas solenoid valve is opened and, simultaneously, an arc is generated, when starting a welding at a gas metal arc welding provided with double gas solenoid valve, in considering that a time of a few minutes is required until forming a gas shield film completely surrounding the welding arc environments after the gas is jetted through the gas nozzle from the solenoid valve, as in FIG. 4, when a torch switch is turned on for starting the welding by firstly opening the gas solenoid valve and, when the shielding gas is started to flow a few minutes later, a wire is fed and, simultaneously, an arc is generated, so that the gas becomes sufficient to shield the arc and the welded base material, even at the welding start portion, and, thereby, welding deficiency is prevented.
Thus, a time where the welding torch switch is made to be on and the shielding gas is jetted, before the wire feeding start time, is called a shielding gas pre-flow time.
However, such a pre-flow time control system have to meet the difficulty of directing a welding torch to a normal position at a state where it is not possible to see a welding portion or a welding torch end, during pre-flow time because, in case where time is elapsed more than one (1) second, an operator completes welding preparation, i.e., the welding torch is directed to a welding start position and the face of the welder is covered by a welding mask so as to be protected from the arc. Even if a welding torch switch is turned on, the arc is not immediately generated and is generated after delaying as much as the pre-flow time of the gas.
Therefore, in a real situation operators change the pre-flow time to less one (1) second even if there is some problem in gas shield at a welding start.
Accordingly, the present invention corrects and supplements welding start in order to overcome the various problems. Therefore, a major object of the present invention is to turn on the torch switch and, simultaneously, the arc is to be generated without difficulty and direct the torch to a normal position even maintaining a sufficient pre-flow time of more than one (1) second.
As a characteristic structure for this, in a gas metal arc welder made by a welding power means, a wire feeding device and a welding torch are made such that, when the torch switch is firstly turned on, only the shielding gas solenoid valve is made to be on whereby only the shielding gas is made to be pre-flowed. The switch is secondly turned on during the pre-flow time, the wire feeding device is operated and, simultaneously, a voltage is applied and an arc is generated so as to be able to weld. When the torch switch is turned off, stop of above described wire feeding device, stop of the shielding gas feeding, and stop of arc are made simultaneously .